Determinants of Calcium Oxalate Supersaturation Levels and Crystallization Rates in Urines from Normal Humans and Stone Formers and Their Relationships to the Etiology and Therapy of Renal Calculi. Renal Calculi are polycrystalline masses found in the collecting passages of the kidney. Calcium oxalate is the primary constituent of over 80 percent of kidney stones and forms the central core (probably the nidus) in 85 percent. Crystallization of calcium oxalate from urine would seem to be of the essence of nephrolithiasis. Supersaturation is an indispensable condition for a crystal to grow from a solution. An understanding of the eitology of kidney stones, and hence possible therapy, would seem to depend on studies of the factors whih determine the levels of supersaturation an rates of crystallization (precipitation) of calcium oxalate from the urines of normal humans and stone formers. C-14 oxalate has been utilized in a new technique developed in our laboratory which can precisely, and very sensitively determine the levels of urinary calcium oxalate supersaturation. More importantly the method lends itself to kinetic studes fo determining the rates of crystalllization of calcium oxalate from human urines Morning urines from both normal humans as well as stone formers are commonly supersaturated (the levels generally being somewhat higher in stone- formers). Crystallization rates have been found to be several times faster in uines from stone-fomers than from "normal humans". Our objective in this research on kidney stones is to elucidate the determinants of supersaturation levels, crystallization rates, and nucleations of calcium oxalate from urines of normal humans and stone formers by utilizing this new C-14 oxalate technique. Preliminary investigations have revealed that nondialyzable materials profoundly influence supersaturation levels as well as crystallization rates. Biochemical characterization and quantitation of these macromolecular regulators in urine should lead to a better understanding of the etiology an possible therapy of renal calculi.